‘Supporters of same-sex marriage have achieved considerable success persuading their fellow citizens — through the democratic process — to adopt their view,” Chief Justice John Roberts writes in his dissent from the Supreme Court’s decision today. “That ends today.”

In most states that already recognized same-sex marriage, the democratic process had been shut down by courts. But this coda is one more blow against the idea that judges should interpret our laws, not write them.

Because marriage is a fundamental right enshrined in the Constitution, five justices of the Supreme Court wrote Friday, every state must recognize it to include homosexual couples. Thus ended their argument.

The problem, naturally, is that whether marriage applies to same-sex couples depends on what marriage is. The Constitution is silent on that question, and judges should be too.

The majority points out how marriage has evolved over millennia — though hardly beyond recognition — and suggests it now must encompass homosexual relationships. But marriage evolved as societies and governments did — not as the result of imperious court decisions. Until the last several years, capped by this decision. This sloppy, arrogant precedent should worry even Americans who rejoice at the result.

Same-sex marriage is not a good idea by judicial fiat, but it is not a good idea by democratic assent, either.

We, of course, do not: Same-sex marriage is not a good idea by judicial fiat, but it is not a good idea by democratic assent, either. The majority of Americans seem to have turned on the traditional, conjugal definition of marriage, but it is the wise one — indeed, the only coherent one.

The majority opinion, by Justice Anthony Kennedy, has almost nothing in the way of constitutional argument for why marriage must extend to a class — people of the same sex — to which it has never been applied, in any society or legal system, until the last couple of decades. Pointing to other decisions striking down restrictions on the historical definition of marriage, as the majority did, does not justify redefining it. Kennedy writes correctly that courts should rule on violations of individual rights, but does not come near explaining how limiting marriage to its traditional definition amounts to such a violation.

The majority offers little more than hand-waving about the slippery slope where all this points. Religious institutions will still have protection under the First Amendment, they say, to “teach” their opposition to same-sex marriage, but the extent of that liberty is not defined. History suggests it could be rapidly curtailed — to prevent religious institutions from having codes prohibiting employees from engaging in homosexual relationships, for instance, or even, someday, forcing the institutions themselves to perform same-sex ceremonies. The majority opinion offers no standard for where freedom of conscience may protect individuals. And if marriage is a fundamental right and the court must update its meaning with the times, what stands between this opinion and legalized polygamy? (A decade or two?)

Those battles will now have to be fought on a legal landscape where invented constitutional imperatives regularly sweep aside democratically written law. The decision is a breathtaking arrogation of political power by the judiciary, a serious loss for the autonomy of the states and the people. Its damage will not be easily or soon undone.